Intravascular filters are used in combination with other thrombolytic agents to treat pulmonary embolism occurring within a patient. Such devices are generally inserted intravenously into a target location of the body (e.g. an artery or vein), and function by capturing blood clots (emboli) contained in the blood stream before they can reach the heart or lungs and cause permanent damage to the body. In the treatment of Deep Vein Thrombosis (DVT), for example, such filters are placed in the inferior vena cava to prevent further blood clotting in the large veins of the lower body. Placement of the filter is typically accomplished percutaneously via the femoral arteries or the jugular vein using a local anesthetic, or by performing a laparotomy with the patient under general anesthesia.
A delivery device such as a sheath or catheter may be used to transport the filter in a collapsed position through the vasculature. In certain designs, the filter can be configured to self-expand when removed from within the delivery device, allowing the filter to automatically deploy within the body. A needle, hook, barb, prong, wedge or other anchoring means disposed on the filter can be used to secure the filter to the vessel wall.
The ability to effectively retrieve the filter is dependent in part on the positioning of the filter within the blood vessel. In some situations, the filter may become offset or tilted if not properly aligned within the blood vessel as it is ejected from the delivery device, causing the filter to asymmetrically engage the vessel wall. Tilting or skewing may also occur within the blood vessel as a result of interference with the delivery and/or retrieval device, or as a result of fluctuations in the vessel wall. Such tilting or skewing can make retrieval more difficult, in some cases requiring additional steps and/or precautions be taken during implantation and subsequent retrieval.